Since Fe—Cr—Al-based stainless steel is excellent in oxidation resistance at a high temperature, the stainless steel is worked into a stainless steel foil so as to be used for the catalyst carrier for an exhaust gas purifying facility (metal honeycomb) of an automobile, a motorcycle, a marine bike, a motor boat, a large lawn mower, and a small electric generator.
Such a metal honeycomb has a honeycomb structure composed of, for example, a flat stainless steel foil (flat foil) and a stainless steel foil formed into a corrugated shape (corrugated foil) which are stacked in alternating layers and which are fixed to each other using a brazing method or the like. A catalytic material is applied to the surfaces of the stacked stainless steel foils, and the resulting metal honeycomb is used for an exhaust gas purifying facility.
A stainless steel foil for a metal honeycomb is desired to have not only oxidation resistance at a high temperature but also excellent brazability when honeycomb forming is performed and not to change its shape when used at a high temperature (if the shape is changed, exfoliation of a catalyst layer occurs or exhaust gas becomes hard to flow due to the crushed cells of a honeycomb structure).
Fe—Cr—Al-based stainless steel, which is excellent in these properties, is widely used in the form of a steel sheet for the members of a stove and a heating furnace and an electric heating element in addition to a metal honeycomb.
On the other hand, Fe—Cr—Al-based stainless steel is not good in toughness of the intermediate material (for example, the hot-rolled steel sheet or the cold-rolled steel sheet) in manufacturing process of a stainless steel foil, as compared with the other kinds of stainless steel. Therefore, it is difficult to manufacture Fe—Cr—Al-based stainless steel, because operation problems and a decrease in yield ratio occur by frequent fracture of the steel sheet during annealing and descaling of a hot-rolled steel sheet or during cold rolling.
As an example of a method for improving the toughness of Fe—Cr—Al-based stainless steel at the hot-rolled steel sheet and the cold-rolled steel sheet, Patent Literature 1 or Patent Literature 2 discloses a technique which improves toughness by stabilizing impurity elements such as C and N in steel through the addition of Ti or Nb. Patent Literature 3 discloses a technique which improves the deep drawability of a hot-rolled steel sheet and the surface roughening resistance of it after working is performed by stabilizing C and N in steel through the addition of Ti and Nb to ferritic stainless steel and by further adding appropriate amounts of V and B.